The long-term objective of the research proposed is to study selected aerodynamic and acoustic measures to determine voice source and respiratory function differences between children and adults during speech. There is limited data of this type for children; yet, the collection and interpretation of voice and respiratory function characteristics of children is already aiding in building comprehensive models of speech production and is already in use as comparison data for disorders of children's speech. Specific goals of the research are to evaluate differences between children and adults on: a) laryngeal valving during speech production, b) spectral characteristics of voice and output function, c) respiratory and laryngeal systems interactions, d) relationships between fundamental frequency and sound pressure level. Each of the proposed studies will include 180 subjects: twenty 4-, 6-, 8-, 10-, 12-, 14-, 16-, 18-year olds, and twenty adults, with 10 females and 10 males in each age group. All subjects will be screened for normal speech, voice, language and hearing. Additionally, they will be required to speak general North American dialect, present no major health problems, be free from allergies or colds on the day of testing, and have no professional voice training. The methods used to assess laryngeal and respiratory function include simultaneous aerodynamic and acoustic techniques. Measures of average oral airflow and intraoral air pressure will be used to estimate translaryngeal airflow and tracheal pressure. A wide-band frequency airflow waveform will be inverse filtered to assess laryngeal function through measures of airflow open quotient, maximum flow declination rate, minimum flow during adduction and alternating glottal air flow. Acoustic measures will include fundamental frequency, sound pressure level, source spectra, formant frequencies and bandwidths. Respiratory function measures will include volume displacements and estimation of tracheal pressure. The research design will be a repeated measures multivariate analysis of variance with two between subject factors of age (child versus adult) and gender (female versus male). Vocal intensity and/or speech task will be the within subject factor for all experiments.